This invention relates to the formation of stub ends for tubes and pipes and, more particularly, to a method of forming lap joint stub ends.
In industry today, it is known to form "stub ends" which are short lengths of pipe having a flange at one end useful for connecting pipes together in the field during construction. That is, in the construction of a chemical plant, for example, relatively short lengths of pipe are provided with a flange at one end. The opposite or non-flanged end of the pipe is then welded in the field to a relatively long piece of non-flanged pipe to provide that long pipe with a flanged end for connecting that pipe to a like flanged end welded to the end of another pipe. The advantage of using stub ends are several-fold. Because the length of pipe used to form the stub end is relatively short, only several inches, it is easier to handle when forming the flanged end than a relatively long piece of pipe, for example, up to 20 feet. The stub ends being short are also relatively easy to store and ship for connection to pipes in the field.
It is old to provide short lengths of pipe with a flange to form stub ends by taking a flat piece of metal, cutting out an annulus having an inside diameter generally that of the outside diameter of the pipe, beveling the edges of the inner circumference of the annulus and welding the annulus to the outside of the pipe. This prior art method of forming stub ends, however, has a number of disadvantages including a relatively large amount of waste of materials, complicated, difficult and time consuming multi-step welding and inspection processes, the lack of integrity of the flange with respect to the pipe, distortion o the flange, and loss of needed properties such as corrosion resistance. That is, in this particular industry, it is common for the stub ends to be formed of a material which has high strength and high corrosion resistance to withstand the pressure and corrosive properties of materials passing through the pipe. Accordingly, the pipe and flange materials are typically formed of relatively expensive materials such as high strength, low alloy nickel alloys. Other alloys could be used. When cutting annuluses from a flat plate, the material cut out to form the center hole of the annulus is wasted as is the material between annuluses. With relatively costly alloys, this makes the process unattractively expensive. Moreover, welding of the annuluses to the pipe ends is a difficult process requiring welding from the backside as well as the front. Several welds are necessary to provide the desired connection. Thereafter, the weld material is machined to provide the appropriate radius between the pipe and flange for strength purposes, and the entire stub end must be heat treated to remove the effects of the heat of the multiple welding processes. The stub end must then be subjected to visual and x-ray analysis to insure the integrity of the weld. This process can take several weeks and results often in a relatively high rate of rejection because of internal porosity and lack of weld integrity. Moreover, the effects of the sequential heating and cooling processes tend to warp the flange contributing to problems of weld integrity and requiring additional heat treating and machining and waste of material. Still further, the effects of weld heat and of heat treating can reduce the corrosion resistance of the material.